Fine Structure and Carotenoid Composition of the Fibrillar Chromoplasts of Asparagus officinalis L.

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Abstract
The spindle-shaped chromoplasts of the ripe fruit of Asparagus officinalis developed from chloroplasts that lost grana and stroma lamellae and accumulated large-sized plastoglobules, most of which transformed into fibrils of exceptionally large diameter. The carotenoid concentration was high in ripe fruits (2520 µg g−1 fresh wt) and consisted mainly of capsanthin, β-carotene and zeazanthin. A. officinalis is only the third species reported to contain both capsanthin and capsorubin. The large diameter of both fibrils and their associated plastoglobules enabled verification that flbrils pass through plastoglobules. Unlike most fibrillar chromoplasts, the plastoglobules remained associated with flbrils even in fully-ripe fruit, and a straight line relationship can be established between plastoglobule and fibril diameter. The presence of more than one fibril developing from a plastoglobule, and the occasional existence of fibrils twisted helically around one another, is interpreted to mean that fibril growth by lateral addition of microfibrils is unlikely. The microfibrillar ultrastructure of Asparagus flbrils was different to that found for Capsicum fibrils, and these differences are illustrated in two models. These differences, however, do not necessarily mean that the fibrils of each species are constructed of different protein sub-units, although the bonding between sub-units is different.